1. Field of the Invention
The present invention relates to a method and apparatus for controlling a communication system. More specifically, the present invention relates to an apparatus and method for allocating identifiers of Base Stations (BSs) in a communication system.
2. Description of the Related Art
In a general communication system, when seamless communication cannot be expected with only the installed existing macro BS, a micro BS, also known as a femto BS, that covers indoor radio shadow areas, is additionally installed to allow indoor Mobile Stations (MSs) to receive desired services over the micro BS, thereby improving the indoor call quality. The micro BS may be differentiated from the macro BS in that it has a smaller coverage and accesses a mobile communication core network using a broadband access network installed in the indoor environment such as a home or office.
FIG. 1 illustrates an example of a micro BS in a communication system according to the related art.
Referring to FIG. 1, a communication system includes a service area 115 of a micro BS 110 (hereinafter referred to as a ‘micro service area’), which is a partial zone in a service area 105 of a macro BS 100 (hereinafter referred to as a ‘macro service area’), which is a relatively large area.
In the communication system, BSs including the macro BSs and the micro BSs receive Physical Cell Identifiers (PCIDs) from an upper-layer management system, and wirelessly transmit synchronization signals and reference signals corresponding to the allocated PCIDs. Then, an arbitrary MS may recognize the presence of its associated macro BS or micro BS by receiving the synchronization signal and the reference signal. Hence, an increase in the number of micro BSs installed in the macro service area may provoke the need for a plurality of PCIDs to distinguish the micro BSs.
However, the number of PCIDs allocable in the entire communication system is a fixed constant. More importantly, the number of PCIDs allocable to micro BSs is determined by excluding PCIDs to be allocated to macro BSs from all possible PCIDs. Therefore, considering the fact that micro service areas are relatively small, a communication service provider, also known as a mobile carrier, reuses allocated PCIDs in a certain distance when the allocable PCIDs are all consumed due to an increase in the number of micro BSs installed in its macro service area. However, when micro BSs reuse the allocated PCIDs, the distances between the micro BSs using the same PCIDs may be undesirably short in the areas where the number of installed micro BSs rapidly increases, for example, in residential areas and commercial areas.
Therefore, Physical Cell Identification (PCI) collision may occur. That is, an arbitrary MS may not be able to distinguish between signals received from two or more micro BSs sharing the same PCID. In this case, installing micro BSs in a related macro service area may be restricted. Accordingly, there is a need for a method and apparatus for efficiently allocating PCIDs in a communication system including micro BSs.